Technical Field
Embodiments of the present disclosure are directed to leadframe packages and methods of manufacturing and assembling leadless packages.
Description of the Related Art
Leadless, or no lead packages are often utilized in applications in which small sized packages are desired. In general, flat leadless packages provide a chip scale or near chip-scale encapsulated package that includes a planar leadframe. Lands located on a bottom surface of the package provide electrical connection to a substrate, such as a printed circuit board (PCB). The leadless packages can be mounted directly on the surface of the PCB using surface mount technology (SMT).
The die in leadframe packages, and in particular quad-flat no lead packages are wire bonded to the ends of the leads in the package. The wire bonding process includes using a force and heat to apply the solder and attach a conductive wire to the lead and a semiconductor die. The leads in the quad flat no lead packages may be cantilevered and the conductive wire is bonded to the free end of the cantilevered lead. The force applied to the free end of the lead during the wire bonding process causes bending and deformation of the lead. Such bending and deformation can cause defects in the connection between the conductive wire and the lead and may lead to premature failure of leadframe packages.
The tooling used to manufacture leadframe packages may include an extension that supports the free end of the cantilevered lead during the wire bonding process, but due to variations in manufacturing, the extension may not properly support the cantilevered end of the lead. For example, if the support is too high, the lead may be biased upward during the wire bonding step, whereas if the support is too low, the lead may be biased downward during the wire bonding step. The extensions on the tooling also do not provide resistance to side to side forces, allowing the cantilevered leads to deform side to side, potentially causing misalignment of the lead and the conductive wire and additional defects.
Leadframe strips, which are composed of an array of units connected with tie bars, may be pre-taped during the manufacturing and assembly process for ease of handling and to aid in preventing encapsulant bleed out. When taped, the bottom surfaces of the leadframe strip are adhered to a tape, but, when the tooling includes extensions that support the cantilevered leads on a leadframe, the leadframe strip cannot be pre-taped because the tape interferes with the extension's ability to support the leads. Thus, when the extension is built into the tooling the leadframe strip is handled without tape until after the wire bonding step.